1.3 The musical life in Den Haag

Public concerts

During the first half of the 18th century, there were not a lot of public concerts yet.  Although The Hague did have a semi-official collegium musicum for some time, most of the collegiae musicae had a more private character than in other, smaller towns. The Hague and The Netherlands in general, did see a lot of visitors and musicians traveling to Germany, France and England. They were invited by the nobility or rich middle-class to play private concerts: Jacob Josef (Francesco) de Lis, a Portuguese tradesman, invited famous musicians such as Jean-Marie Leclair (1697 - 1764) to play for him and his guests. Later in the century, the concerts had probably become more public. In 1773, Charles Burney writes that many foreign musicians stop in The Hague to play a concert before they travel further to England ,Germany or Italy.1

Public concerts that are relevant for this research were the outdoor summer concerts between 1749 - 1751 in The New Vaux-hall, organised by the organist Albertus Gronemann. These concerts were probably one of the first public concerts in The Hague with mainly instrumental music on the programme. In the first year of concerts one of the pieces on the program was the Concerti Armonici by Unico van Wassenaer, although his name was not mentioned. More on this performance will be discussed in chapter 4.

Church

In cities such as The Hague, the organ player of the main reformed church usually had a central place in the musical life. The earlier mentioned Quirinius van Blankenburg was the first organist of the Nieuwe Kerk in The Hague. He had this position between 1702 and 1739 and before that (1687 - 1702), he was the organist of the Court Chapel. He wrote theory books about music, such as Elementa Musica (1738, The Hague) and he also composed music. His Harpsichord and organ book (Clavecimbel- en Orgelboek, Den Haag, 1732) is dedicated to Willem Bentinck. 

Opera

French opera's between 1705 - 1733, mainly Lully. Carlo Ricciotti (Charles Bachiche) mentioned as director of one of the two French opera houses in town. A lot of competition between those two. Both closed down in/around 1733 and it was not until the late 1750's that opera life started again, thanks to the new court of Willem IV and Anna of Hannover. The repertoire consisted mainly of French operas from the 1750's. By 1773, the city also had a German opera house. 

3. Bass playing in music similar to the VI Concerti Armonici

3.1 Bass playing in Italy

Since the influence of Italian music on the VI Concerti Armonici and on concertos written by other composers in Germany and the Netherlands was considerably large, it is worth taking a look at the stiuation of string basses in Italy and the use of double basses in concertos and concerti grossi.  

We know that there many different names used for stringed bass instruments and that the often used 'violone' leads us to several string bass instruments. It could refer to both to 8 foot and 16 foot register instruments and to both violin and gamba-type of instruments.2 As far as it concerns this research, I do not think that the difference between violin-family instruments and gamba-family instruments is vital. Marc Vanscheeuwijck points out that there were many instruments in use that he calls 'hybrids', which have with features from both families.3  He adds that up to the mid-eighteenth century there was a huge variety in stringed bass instruments, not only in names but also in sizes, shapes, set-up and playing techniques. His ideas also correspond with my own findings at the instrument collections of museums of Nuremberg and Vienna and when looking at iconography.  

Unfortunately, very little is known about the musical education of Unico Wilhelm Van Wassenaer. Since he was a nobleman working for the government of the Republic, we do know he was not educated as a professional musician.4 He probably had music lessons from the organist Quirinius van Blankenburg (1654 - 1739). We also know that he played the harpsichord well thanks to a letter by Charles-Philippe d'Albert, Duke of Luynes. His three sonatas for recorder and basso continuo were written between 1713 and 1715 and probably his first compositions. They are dedicated to Friedrich Ludwig, Duke of Würtemberg, who also had music lessons from Quirinius van Blankenburg. The only other compositions that we know of are the motet Laudate Dominum in Sanctis Ejus (date unknown) and the VI Concerti Armonici (1740), which is the subject of this research. 

2. The VI Concerti Armonici 

2.1 The VI Concerti Armonici and their history

Unico Wilhelm van Wassenaer the VI Concerti Armonici between 1725 and 1740, most likely in the Netherlands, where he lived and worked.5 The piece is dedicated to Willem Bentinck.

There is a manuscript score from an unkown copyist, without instrument indications. On the first page, we see 4 treble clef lines, one viola clef line, and two bass clef lines of which the lowest has figures:

Considering 8 foot register string instruments, scholars agree there was a main distinction between small instruments that accomodated soloistic playing and larger instruments for playing a bass line. Around the beginning of the eighteenth century, the rather small violoncello increased in size and musicians started to play it more often vertically rather than horizontally.6 

Until 1675, the name violone was mainly used for instruments in the 8 foot register. After that, violone referred more often to double bass playing in the 16 foot register but since the name contrabbasso was also in use, it could indicate both instruments. Without going into the details about the various instruments that were around, it is worth mentioning that the often used six string violones in G and A had a large range, so players could easily transpose bass lines down an octave. Having this in mind, it is likely that there has not always been a strict distinction between 8 foot register and 16 foot register instruments. Thus, the term violone could not only indicate a large 8 foot instrument or a double bass, but also more generally refer to a string instrument playing in the 16 foot register.

In Corelli's orchestra,  the bass group consisted of a variety of 8 foot bass instruments and double basses playing together, as the violoni were often mentioned seperately from the contrabassi and therefore seem to refer to an 8 foot instrument.7 Although Corelli's group had many different sizes, - depending on the occasions the amount of players could vary from 11 for ceremonies and entertainment up to a 100 for outdoor festivities-  double bassists were also present in the smaller settings of his group.8 Moreover, the orchestra usually didn't include harpsichord but often one or more lutes as chordal instrument.9

There are more indications that double bass was used in concertos and concerti grossi, especially the ones composed by Corelli, Valentini, and also Pietro Antonio Locatelli (1695 - 1764). According to Maunder, they all suggested or expected doubling of all ripieno parts, an additional double bass and an archlute. Valentini explicitly mentions 'contrabassi' in the preface of his Concerti Grossi Op. 7 (Bologna, 1710), in addition to the violoncelli for the ripieno basses. He adds that he had written all the ripieno instrument names in plural because they can be doubled with as many players one would want.10   

Van Wassenaer's wish to stay anonymous was then fulfilled: The first edition, deriving from this manuscript, was published in 1740 in The Hague by the violinist Carlo Ricciotti, on his own costs. The edition consists of seven part books. Although the unkown identity of the composer, the music was sold and several music collectors in The Hague at that time owned a copy of this edition: Jacob Josef de Lis, Nicolaas Selhof and Jacob van Rijswijk.

The title page of that edition gives us more information about the instrumentation, as it reads:
VI CONCERTI ARMONICI a quattro violini obligati, alto viola, violoncello obligato e basso continuo. Dedicati all'illustrissimo signore IL SIGNORE CONTE di BENTINCK.

In 1755, the piece was printed in London by John Walsh with the same amount of part books but attributed to Carlo Ricciotti. Other editions after that are mostly copies from this first edition. It spread through Europe and was attributed to, amongst others, G. B. Pergolesi and G. F. Haendel. Igor Stravinsky used the fourth movement of Concerto II for his ballet Pulcinella, (Paris,1919) probably thinking that it was from Pergolesi. As it goes beyond the aim of this research, I will not go further into the interesting history of editions and attributions of the Concerti Armonici after Unico Wilhelm van Wassenaer's lifetime. R. Rasch and A. Dunning have both written about this topic in great detail.

Looking at the available information, it remains unclear whether Van Wassenaer and Ricciotti expected a doubling of the continuo. Despite the annotations in the music, it is not possible to draw conclusions about Unico Wilhelm van Wassenaer's intentions and ideas concerning the performance of this piece and his music in general.

Added to this manuscript, there is a note in Van Wassenaer's own handwriting about the piece. Throughout the manuscript score, we find little annotations from his hand, too. His words tell us some things about occasions and the players surrounding him but they also reveil how he judged his own music:

In The Hague, there were at least five gentlemen who frequently played contre-basse in the the Court Chapel in the years 11 As there is very little information to be found about double bass players in the decades before, this topic would need further research. 12

1. Unico van Wassenaer and the music around him 

1.1 Unico Wilhelm van Wassenaer and his environment

Count Unico Wilhelm van Wassenaer (1692 - 1766) was a nobleman from the Netherlands. He was born in the castle of Twickel, in the province of Overijssel. His father Jacob was an ambassador of the Republic of the Seven United Netherlands, so the family also owned a house in the capital The Hague. At the age of 15 Unico joined his father to the court of Johann Wilhelm in Düsseldorf for a stay of two years. This court was known for its rich musical life and it seems likely that he heard music from Agostino Stefani, Arcangelo Corelli there.

The surviving instruments from the 18th century that were made in the Netherlands are unfortunately not numerous. There is a double bass made by Johannes Theorodus Cuypers (1724 - 1808) around 1750, probably in The Hauge. This instrument has been owned by the Royal Concertgebouw Orchestra is now owned by bassist Robert Franenberg and probably the only Dutch double bass from the early and mid-18th century.

As the previous mentioned double bassists from the Court Chapel were of German origin, there were probably German instruments around, too. The topic of specific instruments and players will need further research that goes beyond the scope of this paper.

After returning to the Netherlands in 1709, Unico Wilhelm moved to the family house in The Hague and attended the University of Leiden to study law. After the death of his father, he inherited the estates of Twickel and the title Lord of Twickel. Like many noble young men, Unico Wilhelm undertook a grand tour through Europe between 1717-1719. He visited Germany, Paris and probably other cities that were a usual destination for that time: Rome, Venice, Naples, Florence, Vienna and Prague. 
After he got married in 1723, he moved with his family from Twickel to The Hague, a house on Noordeinde that is unfortunately not there anymore. He had a career in the government of the Dutch Republic and had high postitions as an ambassador. In 1745, he and his wife Dodonea moved to a large house on the Kneuterdijk in The Hague in 1745, where he died in 1766.      

3.3 String bass instruments in the Netherlands

In Dutch musical encyclopedias and music theory books from the 18th century, we find a great variety of names for the low stringed instruments that derived from Italian, French and Dutch language: Basse double, Double basse, Contra Basso, Contra Violone, Basfiool, Strijkbas, Viola basso, Violoncello, Bassetto, Basse and even more variations seem to all have been used. The authors often point out that more names were used for the same instrument, sometimes causing more dazzle.13  In her study, Anneke Hogestijn connects these names to Dutch music and scores or parts written in Dutch. She concludes that there were five kinds of bass instruments. I interpret her findings a bit differently and make the following distinction:
 

• The viola da gamba that seems to be similar to how we know it today, with sometimes 6 and sometimes 7 strings; 
• Small bass violins called basset(to), kleine basviool, kleine violoncel and viola basso. It had 4 to 6 strings and sometimes had straps, perhaps to accomodate horizontal playing rather than vertically between the legs; 
• Bass violins that was called violoncel, violoncello, basse de violon, basviool, bas, basse and strijkbas. They were larger and had no straps. If solos were played on this instrument the tenor clef was used in the part.
  
• Bass violins that were called basse double, basse-double, double basse, groote violoncellen, and violone. They are described as larger violoncellos or small contrabasses and often, the term 'dubbelde bas' is added to the description. 
• Largest string instruments called contrabas, contrebas, contrabasso, contra-violone and also violone. Interestingly, they are not described bass violins but as instruments that are an octave lower than the bass, bass violin or violoncello.

This list shows that the term violone is ambiguous and seems to belong to two different instruments. Hogestijn writes that the term 'basse double' has been only found once in musical scores in parts, which is surprising if this instrument was different from a violoncello and a contrabass. Another option is that the word list is misleading: Basse double could just be a translation of 'dubbelde bas' or the other way around, which would mean that the term just another instrument but just about doubling the bass part, either in the 8 foot or in the 16 foot register. The term 'dubbelde bas' does not necessarily refer to another instrument: In Verschuere Reynvaen uses the term to describe a bass line played on the organ with the left hand and the pedals.14

In Dutch scores and parts just the words bas, basso and basse prevailed, without further specifiation of instruments.15 The first specific indication for a double bass was probably by Antonio Mahaut (1719 - 1785) in Sinfonia II from his VI Sinfonias Op. 2 (Amsterdam, 1751). 

From 1736, double bass players were listed in orchestra's and ensemble in the Netherlands, but paintings from the late 17th century and early 18th century show that large string instruments were already in use for at least some decades before that. Although those instruments look almost as tall as double basses, it is very well possible that they had a higher tuning due to the string making techniques and developments in the last decades of the 17th century.16   

4. Performance practise of the VI Concerti Armonici

4.1. During Unico van Wassenaer's lifetime

The VI Concerti Armonici have certainly been played at the collegium musicum gatherings by Unico van Wassenaer himself, Carel and Willem Bentinck, Ricciotti and their friends. R. Rasch reconstructs the members and guests of the collegium musicum around 1725 and suggests a a small group with one voice per part: Carlo Ricciotti certainly played the first violin part; Van Wassenaer himself and Willem Bentinck could both have played one of the violin parts or the harpsichord.17There might have been a performance at the Court in Paris in the year 1746, when Unico van Wassenaer was sent to France for political negotiations. The only information about this performance is a letter from the Marquis of Argenson, who wrote in his memoirs that a piece by Van Wassenaer was performed and that is was "good as the music by Corelli".18     

Surely, a public performance has taken place at the Nieuwe Vaux-hall in The Hague in August 18, 1749. This was probably the only public concert in the Netherlands of the Concerti during Van Wassenaer's lifetime as there was not yet a culture for concerts with instrumental music. Apparently, Unico van Wassenaer still wanted to stay anonymous so the piece was in the newpaper advertisement as "composed by an honourable gentleman". The Nieuwe Vaux-Hall was a public hall for entertainment, such as balls and games, with a concert garden in which summer concerts took place that were usually concluded by festive fire works.19 The concerts were organized by the violinist and organist Johannes Albertus Groneman between May 1749 and September 1751. It's short existence probably had to do with competition from the more serious venue the Ouden Doelen in Den Haag. Unfortunately, the players or ensembles have not been listed which means that, considering the instrumentation, there is no information on that.

Although copies of the first edition of the music were owned by several music collectors, there is no evidence that the music has been performed elsewhere in the Netherlands before 1766.

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1. 2. The collegium musicum

Unico van Wassenaer was part of a collegium musicum in The Hague. The Netherlands knew many collegiae musicae with different formats or purposes. Some of them had a closed, informal character and consisted of amateur musicians from the upper classes: One had to be invited to become a member, the members gathered in the large houses of their whealthy members and the concerts were not public. Others had a more official status and were sometimes recognised by the city council. This meant sometimes that the city provided in a rehearsal location and that the collegium was asked to provide music for festivities. 

The collegium musicum which Unico van Wassenaer was a member of was formed by amateur musicians from the middle and upper classes who wanted to play music together. A main member this collegium was the professional violinist Charles Bachiche (1681 - 1756), also known as Charles Bacciccia or Carlo Ricciotti . He was the first violinist and probably the only professional musician. He is also the publisher of the first edition of Unico van Wassenaer's VI Concerti Armonici. 

Others members of this collegium musicum in The Hague were the brothers Willem Bentinck (1704 - 1774) and Charles of Carel Bentinck (1708 - 1778). They were also nobility and friends of Van Wassenaer's family. Willem Bentinck and Unico Wilhelm van Wassenaer were friends from 1718 and Unico dedicated the VI Concerti Armonci to him. Willem had violin lessons from Carlo Ricciotti and harpsichord lessons from Quirinius van Blankenburg.
The other people invited to the collegium musicum gatherings were nobility and ambassadors from England, France and Italy.

2.2 Van Wassenaer's style

Unfortunately, it is not known what Unico Wilhelm van Wassenaer thought of other composers and which music inspired him to write the VI Concerti Armonici. This is probably due to the fact that he did not want to be known as a composer and therefore did not write about his musical ideas. Besides that, only a small part of his own collection of music of other composers has been preserved or listed. This makes it hard to reconstruct his possible influences and preferences. When hearing Van Wassenaer's VI Concerti Armonici, the first impression could be that the pieces are concerti grossi in the composing style of Arcangelo Corelli (1653 - 1713), Antonio Vivaldi (1678 - 1741) and Guiseppe Valentini (1681 - 1753). Van Wassenaer knew and probably played a lot of music from these composers.21 Yet, a closer look shows that Van Wassenaer combined several styles and elements to create his own signature.

The music that was played in the collegium musicum was probably often Italian. In the first decades of the 18th century, the Italian concertos and concerti grossi were popular in the Netherlands. Many Italian concertos were printed by Estienne Roger in Amsterdam and then bought by amateur musicians from the higher and middle classes.22 

Yet, the early concerti grossi were not only composed by Italian composers. The style and ideas from Corelli and Vivaldi had a lot of influence on German and Dutch composers. There are the XII Concerti a quattro op. 7 (Amsterdam, 1704) by Henrico Albicastro (c. 1660 - 1730) and the Concerto Grosso op. 2 by Willem De Fesch (1687 - 1761) was first published in 1717 in Amsterdam, by Etienne Roger.An impressive example of early concerti grossi from outside Italy are the twelve concerti from Außerlesener mit Ernst und Lust-gemengter Instrumental-Music (Passau, 1701) by Georg Muffat, composed in the 1680's. It has a rich instrumentation with more middle voices than most of the Italian concerti grossi.

4.2. Public concerts vs. playing at home

There was probably a difference between the collegium musicum gatherings and public performances, since they served a different purpose.The concerts of the collegium musicum were mostly private evenings of the elite to enjoy themselves and perhaps impress each other. There was no clear distinction between players and audience. 

Public concerts were meant for a paying audience that wants to be entertained. This implies that the ensemble sound has to be heard well and therefore is concerned with projecting well into the audience. The amount of players and instrumentation of the basso continuo group would depend on the instruments at the venue and the professional musicians available. This was probably also the case in a concert venue such as de Nieuwe Vauxhall in 1749.23   

4.3 After 1766

Thanks to the edition of John Walsh from 1755, the music was spread in England where it became a popular piece under the name of Ricciotti. From the second half of  the 18th century the piece has been performed many times in England. There have certainly been several concerts in Cambridge during the 1780's, such as one on 28th of June, 1782 at the Trinity Concert Hall.

During the 19th century, at least three different copies of the music were also spread throughout Europe. Since the music was attributed to several composers, it is very difficult and often impossible to recontruct the performances. Furthermore, investigating the 19th-century performance practise of this music would go beyond the scope of this research.

Court
Between 1592 - 1795 The Netherlands was the Republic of The Seven United Netherlands. For most of the time, the Republic had a stadtholder (stadhouder) with a court in The Hague. However, there was no stadtholder from 1702 until 1747, when Willem IV was inaugurated. 
Stadhouder Willem IV and especially his wife Anna of Hannover were interested in theatre and music. From 1750, there was a small court chapel of around 8 musicians: 5 violinists, a cellist, a double bassist and a bassoon player. All of them were from Germany and some of them had worked at the court of Anna of Hannover in Leeuwarden before. The double bassist Johann Heinrich Gundelach (1715 - 1779) had worked there as a horn player before coming to The Hague. The violinist Johann Keller was probably the concertmaster/kapelmeister/leader. It seems that the group of 8 players was the formation for daily use: entertainment during dinners and bals. For some festivities, a larger number of musicians was hired for an orchestra. The biggest group seemed to have had to around 35 players, on the inauguration of stadtholder Willem V in 1766. By that time, the court attracted many well-known foreign musicians and had visits from Georg Friedrich Händel and Leopold and Wolfgang Amadeus Mozart.  

3.2 Bass playing in Northern Europe

 
In North and Middle Europe, the rise of the violoncello took more time than in Italy and during the first decades of the 18th century, 6 string violones tuned in G were used in Germany and Austria.24  From the 1720's, the violoncello tuned fifths was used more and more throughout Europe, but up until the 1750's, the size and the tuning of the violoncello were not standardised.25 The same counts for the double bass. Leopold Mozart writes in his Versuch einer grundlichen Violinschle (Augsburg, 1756) that both the violoncello and the double bass were made in different sizes and could have five or six strings. 

Considering the role of the double bass in in instrumental music in the beginning of the 18th century, Marc Vanscheeuwijck states that in general, the instrument was rarely used in that period26. Judy Tarling writes that “where the cellist plays many notes, the double bass player should sketch the main harmonic structure, without filling in all the beats.”27 She refers to an example from Quantz's treatise. Reading his words, in can be very well possible Quantz' suggestion does not come from a musical idea but rather from his concern with the bass player's ability to play fast notes:

"If in a bass part passage-work appears which, because of its great rapidity, the double bass player is unable to execute distinctly, he may play only the first, third or last note of each figure, whether they are semiquavers or demisemiquavers. In each case he must determine which notes are the principal notes in the bass melody. (…) Except in passage-work of this sort, however, which some find too difficult to play rapidly, the bass player must omit nothing.28"

Considering the use of double bass in concertos, we find in Quantz' Treatise the practise that is used a lot nowadays in solo concertos and concerti grossi: The double bass only plays in the 'ritornellos', the tutti moments when usually all the other instruments join in to play the theme.29 

This does not mean that the double bass was not used before the 18th century or in other genres of instrumental music. There are pieces from beginning of the century and even from the late 17th century, in which the double bassist has something to do. Georg Muffat explicitly mentions in his Außerlesener mit Ernst und Lust-gemengter Instrumental-Music (1701) that the basso continuo part can be doubled with double basses and violones, according to the taste of the director.30 Like Valentini, he suggests doubling of the concerto grosso parts. These concertos by Muffat are particularly interesting, because they do not have the ritornello form where Quantz referred to.  

3.4 The basso continuo group in the Netherlands

Despite the evidence in iconography, Dutch music theory books from the 18th century do not mention the double bass or the violone as an instrument to double the basso continuo line with. The name violone does appear on musical parts from the first half of the century, often in music where the violoncello is also listed and has a seperate part.31 This can be seen in the 12 Sonatas op. 4 by Willem de Fesch.

De Fesch' VI Concerti op. 2. has almost the same instrumentation as Van Wassenaer's VI Concerti Armonici, the only difference being that De Fesch explicitly asked for an organ as continuo instrument. Furthermore, there are similarities in the way of writing for the violoncello and for the basso continuo.
In both pieces, the basso continuo part is sometimes written an octave lower than the solo violoncello.This way of writing makes way for the solo violoncello to claim its role as solo instrument within the piece. Maunder argues that this is an indication that there should not be a double bass instrument playing along. He also refers to the reprint of Valentini's concerti in Amsterdam in 1714. Roger made some changes that especially concerns the basso continuo: he added an organ part to the solo violoncello; omitted the extra figured ripieno bass part and changed the ' violoncelli o contrabassi' into 'basso'. Maunder concludes that this indicated a Dutch performance practise in which lutes and double basses were not used for this kind of music. He adds that it was probably played with one player per part and a second violoncello or bass violin in the ripieno bass group.

However, there are indications that oppose this standpoint.
First of all, the number of parts does not necessarily lead to the used number of players, especially not in the basso continuo group. In iconography we often see the string bassists next to the keyboard, reading the parts over the shoulder of the keyboard player. In that case, the number of parts mainly say something about the minimum amount of players used.

Secondly, there are reasons to believe that the bass line should be doubled with a larger instrument than the solo violoncello. The larger one was used to double the bass line with and the smaller one was used for solos. As shown in the previous paragraph, this was propabably also the case in the Netherlands. The violoncello used for solos was considered the smaller version of the 8 foot string basses.

This leads to the conclusion that in these concertos by Willem de Fesch and Van Wassenaer no doubling or doubling with a large string bass instrument playing in the 8 foot register are legitimate options. From a performer's point of view, the solos played on the violoncello will more likely come across if there is not exactly the same instrument doubling the basso continuo line.

Moreover, the theorbo was probably still used in the Netherlands first decades of the 18th century. In his Elementa Musica from 1739, Quirinius Van Blankenburg did not only list the theorbo as a continuo instrument, he explicitly mentioned that the theorbo is still used:

First of all, The Concerti Armonici lack the typical contrasting setting of a few concertino players accompanied by the ripieno players. Although the first and second violin and the violoncello have the most soloistic parts, especially in Concerto III, they are not the obvious soloists throughout all the Concerti. 

Secondly, the form and markings such as Da Capella follow the late 17th-century sonata di chiesa and sonata da camera traditions. He avoids symmetrical phrases or the ritornello-style of writing that we often see in concertos by Vivaldi and Valentini, in which the whole ensemble repeats a solo line.32  

Furthermore, he uses the string instruments in an unconventional way by joining and seperating lines on unexpected moments, so that the music varies from being a three, four or five-partpiece. The melodies often meander through different parts, instead of being started and finished by the same instrument. Perhaps the idea to have four different violin parts could have derived from the concertos by Valentini and Vivaldi, but Van Wassenaer's writing for the third and fourth violin and the viola give the whole ensemble a colour that is different from their Italian style. Unlike his contemporary Willem de Fesch, Van Wassenaer was just a bit influenced by Vivaldi's music: Van Wassenaer's violin parts are less virtuosic in the sense that they do not have a lot of fast runs and jumps that can only be played on a violin. The melodies are written more vocally and are therefore closer to the style of Corelli but Van Wassenaer's use of harmony and dissonants resembles more late-baroque style.33 Nevertheless, De Fesch' twelve concertos op. 2 and op. 3 (Amsterdam, 1717) could have been an inspiration for Unico van Wassenaer, as they are a relatively early example of concerti grossi from the Netherlands.

Another interesting aspect of Van Wassenaer's music is his use of counterpoint and the way he constructs fuges, which both relate to the late 17th-century church and chamber sonata. This can also be an indication of some German influences such as Georg Muffat's concerti grossi from Außerlesener mit Ernst und Lust-gemengter Instrumental-Music. Although this music also clearly has a French influence that Van Wassenaer's Concerti Armonici lack,34 and it is uncertain if he knew Muffat's concerti, it could nevertheless explain his attention for the middle voices and his use of counterpoint.

Other concertos that Van Wassenaer probably knew are the concertos by Johann Christian Schickhardt (c. 1681 - c. 1762),35 Henrico Albicastro (c. 1660 - 1730)36  and Francesco Venturini (c. 1675 - 1745).37  Stylistically, there is also ressemblance with the Twelve Concerti Grossi op. 6 by Georg Friedrich Händel (1685 - 1759), but since the first publication was in 1739 (London, Walsh) it is not possible that Van Wassenaer used this piece as an example. 

Although the VI Concerti Armonici seem to be Dutch concerti grossi, there are indications that the piece does not completely fit in that genre. Thus, the Concerti Armonici do not have the logical moments for a double bass to drop out or join in again, such as many concertos and concerti grossi do.

Since he was probably Unico Wilhelm van Wassenaer's teacher and therefore a direct musical influence, Van Wassenaer probably knew about this opinion. 

Lustig writes about performing a concerto that the accompanying instruments usually are a couple of violins, alto and bass and that those can be doubled according to the occasion (p. 165 - 166. Muzijkale Spraakkonst, 1754). Some general rules about accompanying. He also mentions lutes when he writes about concertos for 'clavieren en luiten' on p. 167.  

(...)

To sum up the points from this chapter, there was a large variety of string bass instruments in Italy and in the Netherlands during the first half of the 18th century. It is likely that in the Netherlands, the violoncello was often a rather small 8 foot register instrument and that a larger 8 foot instrument was used to play bass lines with. Double basses, playing in the 16 foot register, were certainly used in the Italian instrumental repertoire that influenced many Dutch composers such as Van Wassenaer. Furthermore, there are many indications in iconography that double basses were used in instrumental music and chamber music settings. From 1736, double bassists were sometimes listed and definitely part of ensembles from the 1750's. 

 
Concerning Van Wassenaer's VI Concerti Armonici, doubling the bass line with a string instrument in the 8 foot register or in the 16 foot register are both legitimate options. The instrument in the 8 foot register was probably an instrument that was larger than the violoncello used for the obligato part.

Theorbos were still used and could have very well been part of the basso continuo group in this music.

Further to IV. Experiments